In the above technical field, in order to accelerate attribute aggregation processing, a technique disclosed in NPL 1 uses an index described therein (hereinafter, a lightweight index) in the aggregation processing. The technique disclosed in NPL 1 omits scanning of records by using the lightweight index and reduces an input/output (I/O) amount of data to/from a storage and a computation amount. NPL 1 discloses such the technique of accelerating attribute aggregation processing.
For example, the technique described in NPL 1 typically performs query processing as in FIG. 20 with respect to processing of a query 1900 illustrated in FIG. 19 for calculating (selecting) a maximum value (MAX) among heights (Height) of employees (Staff). In other words, the technique described in NPL 1 executes attribute selection 2002 on table data 2001 and finds a solution 2003.
As illustrated in FIG. 21, the technique described in NPL 1 horizontally partitions large table data 2101 into a plurality of partitions called blocks 2111 to 2113 and saves the blocks respectively assigned with lightweight indexes 2114 to 2116. Then, the technique described in NPL 1 scans the lightweight indexes 2114 to 2116 with respect to Height attribute (height) for the blocks, acquires maximum values 2117 to 2119 of the heights in the blocks, and computes (selects) a maximum value among the acquired maximum values. The technique described in NPL 1 computes a maximum value of the heights in the entire table data 2101 based on the above-described operation. An I/O amount necessary for a series of processing at this time may be an I/O amount in the scanning of the lightweight indexes for the respective blocks. In addition, processing of computing a maximum value may be performed by computing a maximum value from the maximum values obtained from the respective blocks. Consequently, the technique described in NPL 1 is faster than simple processing which requires scanning and computation for all blocks.